Enable mbtree by default, and remove it from presets

ffpresets/libx264-baseline.ffpreset

ffpresets/libx264-default.ffpreset

ffpresets/libx264-fast.ffpreset

ffpresets/libx264-fast_firstpass.ffpreset

ffpresets/libx264-fastfirstpass.ffpreset

ffpresets/libx264-hq.ffpreset

ffpresets/libx264-ipod320.ffpreset

ffpresets/libx264-ipod640.ffpreset

ffpresets/libx264-lossless_fast.ffpreset

ffpresets/libx264-lossless_max.ffpreset

ffpresets/libx264-lossless_medium.ffpreset

ffpresets/libx264-lossless_slow.ffpreset

ffpresets/libx264-lossless_slower.ffpreset

ffpresets/libx264-lossless_ultrafast.ffpreset

ffpresets/libx264-main.ffpreset

ffpresets/libx264-max.ffpreset

ffpresets/libx264-medium.ffpreset

ffpresets/libx264-medium_firstpass.ffpreset

ffpresets/libx264-normal.ffpreset

ffpresets/libx264-placebo.ffpreset